Thai authorities have arrested two men charged with human trafficking, police said on Tuesday, following the discovery of 134 suspected victims in southern Thailand at a time when the military government is under international pressure to tackle the crime.

The two Thais were charged in relation to a group of 53 men found on Saturday at a rubber plantation - 38 from Bangladesh and 15 Rohingya, a mostly stateless Muslim minority from western Myanmar.

"The two men have been charged with trafficking and bringing foreign labor into the country illegally," a senior police official, who declined to be identified, told Reuters.

He said police were still looking for the gang leaders.

If found guilty, the men face up to 10 years' jail.

Thailand was downgraded in June to the lowest "Tier 3" category in the U.S. State Department's 2014 Trafficking in Persons Report for not fully complying with the minimum standards for eliminating trafficking.

Prime Minister Prayuth Chan-ocha, the army chief who seized power in a May coup, has vowed to "prevent and suppress human trafficking".

A human rights group said the latest discovery showed little progress had been made.

"Although the arrest of alleged traffickers can be viewed as a positive step, the discovery of these groups shows that trafficking routes in Thailand are still very active," Sunai Phasuk, Thailand senior researcher at Human Rights Watch, told Reuters.

"Regardless of the promises of the junta, nothing seems to have been done in concrete terms to stop trafficking gangs."

The discovery is in keeping with what a leading advocacy group says is an alarming rise in "forced departures" from Bangladesh.

The 134 people have been found since Saturday in Phang Nga, said Churin Kwanthong, head of the Phang Nga office of the Ministry and Social Development and Human Security. The province is popular with tourists,

The 53-strong group was found at a rubber plantation in the province. He said authorities were interviewing the remaining 79, who were discovered on a remote island on Monday.

"We have to wait for further information on this group to see if they were tricked in to coming or whether they came of their own volition," said Churin.

"If they were tricked then we would also consider them victims of human trafficking".

Reuters reported last year how thousands of Rohingya were held and sometimes tortured by traffickers at jungle camps in southern Thailand.

Tens of thousands of Rohingya have fled Myanmar since 2012, when violent clashes with ethnic Rakhine Buddhists killed hundreds and made about 140,000 homeless.

Sunai at Human Rights Watch said Thailand's efforts to combat trafficking amounted to little more than lip service.

Government spokesman Yongyuth Mayalarp defended its record.

"We are talking about cooperation on how to combat human trafficking all the time, including during Prayuth's visit last week to Myanmar," Yongyuth said. "Prayuth has asked all agencies to pay particular attention to this issue."